Relational databases usually enforce relevant organizational business rules. This aspect is ignored by current database reverse engineering approaches which only focus on the extraction of the structural part of the conceptual schema. Other database elements like triggers, views, column constraints, etc. are not considered by those methods. As a result, the generated conceptual schema is incomplete since integrity constraints and derivation rules enforced by the database are not represented. In this sense, this paper extends existing approaches by enriching the generated (UML) conceptual schema with a set of OCL integrity constraints and derivation rules inferred from the database schema. Our method has been implemented in a prototype tool for the Oracle database management system.

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Extracting UML/OCL Integrity Constraints and
Derived Types from Relational Databases
Valerio Cosentino
Salvador Martínez
{valerio.cosentino, salvador.martinez}@mines-nantes.fr

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Outline
 Introduction
 Approach overview
 Model Extraction
 Constraint Extraction
 Conclusion and future work

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Introduction
Relational databases play a key role in most organizations
 They store relevant information according to:
–Schema: data structure definitions and relations
–Integrity constraints (declarative, operational):
implementation of organization policies/business
rules
 These constraints should evolve together with the
organization policies

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Introduction
 Discovering/understanding the business rules in a db is:
–Time-consuming (querying/browsing the database)
–Error-prone (manual analysis)
–Tailored process (each SQL vendor offers slight
variations for the standard language)
 Model Driven Engineering offers:
–Homogeneous representation (schema + constraints)
–Higher abstraction level (no SQL vendor specificities)
–Automatation of repetitive activities (extraction of
schema and constraints)

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Approach overview
 Model Extraction translates tables, relations and views
into UML classes and associations
 Constraint Extraction focuses on inferring the OCL
expressions required to complement the UML model

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Model Extraction
 Mappings:
– Tables → classes
– Views → derived classes
– Columns → class's attributes
– Database data types → UML data types
 CHAR(n), VARCHAR2(n) → String
 Integer, Float, Date → Integer, Real, Date
 Number(precision, scale) → if precision = 0 Integer else Real
– Foreign keys → associations between classes
– SQL queries → associations' cardinalities

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Model Extraction
 Example: human resource database

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Constraint Extraction
 Declarative constraints:
– PRIMARY KEY
– UNIQUE
– NOT NULL
– CHECK
 Operational constraints:
– Triggers: PL/SQL - SQL code automatically executed in
response to certain database events
 Key elements: SQL-to-OCL and PL/SQL-to-OCL
– they map SQL and PL/SQL constructs to OCL

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Declarative constraints
 Declarative constraints:
 Example:

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SQL to OCL
 Projection and selection:
 Example:

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SQL to OCL
 Join:
 Example:

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SQL to OCL
 Group and having clause:
 Example:

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Triggers
 Triggers are composed by:
– Triggering event: SQL statement, database or user event
– Trigger condition (optional): boolean expression
– Triggered action: PL/SQL block (procedural and SQL code)
 They can be executed: instead of, before or after
performing the triggering event

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PL/SQL to OCL
 All triggers that embed in their action a PL/SQL
statement raising an exception defined by the user are
classified as business-relevant
– Two ways to use user exceptions:
 RAISE statement (Override an already-defined exception)
 RAISE APPLICATION ERROR statement
 These exceptions are generally nested in conditional
statements. For each exception, the conditions
triggering the exception are mapped to an equivalent
OCL expression.

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PL/SQL to OCL
 Trigger:
 Example:
SQL to OCL mappings

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Refining OCL Constraints
 UML stereotype mechanisms are used to annotate each
OCL constraint extracted from a Trigger with the
information of the events that apply to it (insert,
update, delete)
 Annotated OCL constraints can be merged together
when:
– they are semantically-equivalent
– they are applied to different events

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Conclusion and future work
 MDE benefits:
– Modular and generic approach
– Automatic extraction of the organization policies in
databases
 Future work
– Test the framework on a real database application
– Extend the OCL language with additional libraries for
representing calendar-based constraints
– Integrate the extracted business rules with those ones
extracted from other system's components

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Questions